Extrusion of seamless tubing

ABSTRACT

Improvement in the process of hot extruding metal tubes in a hydraulic press, in which the metal billet inserted into the press has been pierced to a bore diameter largly exceeding that of the extrusion mandrel and the force of the press is applied in a progressive manner.

finite States Patent 1191 Hubert [54] EXTRUSION OF SEAMLESS TUBING [75] Inventor: Ren Hubert, Boulogne sur Seine,

France [73] Assignee: Cefilac, Paris, France [22] Filed: Oct. 16, 1970 [21] App1.No.: 81,570

[30] Foreign Application Priority Data Nov. 5, 1969 France ..6937995 [52] US. Cl. ..72/264, 72/370 [51] Int. Cl. ..B2lc 23/04, B21b 17/02 [58] Field of Search ..72/264, 265, 266, 267

1 1 Apr. 3, 1973 Primary ExaminerCharles W. Lanham Assistant Examiner-R. M. Rogers AttorneyWebb, Burden, Robinson & Webb [57] ABSTRACT Improvement in the process of hot extruding metal tubes in a hydraulic press, in which the metal billet inserted into the press has been pierced to a bore diameter largly exceeding that of the extrusion mandrel and the force of the press is applied in a progressive manner.

5 Claims, No Drawings EXTRUSION OF SEAMLESS TUBING The invention is directed to an improvement in a method for extruding metallic seamless tubes from a hot hollow billet.

According to the known practice for extruding such tubes with one of the usual lubricants, the container of the extrusion press receives a hot cylindrical hollow billet, the outside diameter of which is slightly smaller than the inside diameter of the container, and the bore diameter of which is larger than that of the extrusion mandrel by only a few millimeters. A lubricant is distributed along the lateral surfaces of the container, the mandrel and/or the billet and between the billet and the die. The mandrel is inserted into the billet bore coaxially with the container and the whole force of the press is applied. When being deformed, the metal occupies the whole space available in the container and flows out through the ring-like aperture between the mandrel.

and the die closing the downstream end of the container. 7

By selecting a bore with a diameter only slightly larger than that of the mandrel, it is possible to give to the billet the largest weight compatible with a short length. This, however, results in several drawbacks.

If the billet and the mandrel are not coaxial, when the mandrel is inserted into the billet, the small clearance between these two elements, combined with their relative motion, may cause the billet to contact the travelling mandrel with the result that the lubricant may be scraped off. This is true regardless of whether the lubricant has been applied into the billet bore or onto the lateral surface of the mandrel. This causes a nonuniform distribution of the lubricant along these surfaces. The result of the nonuniform distribution can be any one or more of irregular metal flow during extrusion, local seizings, excessive die wear, defective inside surface condition and poor concentricity of the inside and outside surfaces of the product.

These drawbacks occur with a particular frequency on horizontal extrusion presses, where the billet rests on the lowest generatrix of the container, so that the bore of the billet and mandrel cannot be accurately concentrically aligned, however small the clearance between them. Additionally, when the whole force of the press is immediately applied to the ram, the metal begins to flow through the die before the billet has filled up the space available in the container, i.e., before the mass of metal has been distributed coaxially within the container. The initial flow then is generally initiated in the lower part of the mass of metal to cause the front end of the tube to be slanted or wedgeshaped. This creates a force directed upward, which forces the front end of the mandrel out of concentricity. Since the upper part of the die aperture is not occupied by metal, an uncontrollable part of the lubricant between the billet and the mandrel can escape to create an insufficient amount of lubricant for the balance of the extrusion. The tube produced under these conditions has an initial eccentration, which may occur along its entire length and it also may show surface defects caused by the uneven lubrication.

Another drawback in the use of a bore diameter only slightly larger than the mandrel diameter lies in the close association between the bore diameter and desired tube inside diameter. As many piercing tools are needed as there are mandrel diameters, and tubes with different bores cannot be made from billets having only one bore diameter.

It is known that the force required for starting an extrusion operation, and referred to as the starting or overpressure, is larger than the force required for the balance of the extrusion, normally referred to as the running pressure. Therefore, the nominal force of the press is incompletely used during a substantial portion of the working time. In addition, the initiation of the extrusion causes an initial wear of the tools, which limits their use for producing a long extrudate.

The present invention concerns improvements in the processing by hot extrusion of tubes in metals difficult to deform; the improvements permitting the extrusion of tubes with a greater length, a better concentricity and a smoother, substantially defect free surface condition- At the same time, my process permits more complete use of the force of the press. More specifically, my invention improves the concentricity of the resulting tube and the lubrication for the extrusion, lowers the starting pressure appreciably and permits the use of a single bore diameter for extruded tubes of several diameters.

According to my process, a billet is coaxially pierced to a bore diameter noticeably exceeding the mandrel diameter. The billet is inserted into the container of an extrusion press and then a progressively increasing force is applied to the billet. This progressively increasing force results from the controlled opening of the valve admitting thehigh pressure liquid into the press cylinder or cylinders.

In my process the diameter of the billet bore exceeds the mandrel diameter by at least 5 percent of the difference between the container and mandrel diameters, preferably 20 percent but not more than 30 percent of the difference between container and mandrel diameters. For example, if a billet is to be extruded from a 300 mm (1 1.8 inches) container with a mm (3.94 inches) mandrel, it will be pierced to at least l 10 mm (4.33 inches) [100 mm 5 percent X (300 mm-lOO mm The most preferred bore diameter would be mm (5.5 inches) 100 mm 20 percent (300 mmlOO mm) The maximum bore diameter would be mm (6.30 inches) 100 mm 30 percent X (300 mm-l00 mm) Therefore, if the billet and the mandrel are coaxial, clearance on the bore diameter would be at least 10 mm (0.39 inch) and preferably 40 mm (1.58 inches) and would not exceed 60 mm (2.36 inches).

The progressive opening of the valve admitting the high pressure liquid advantageously results in a linear increase in pressure achieving the maximum pressure in the press cylinders after 0.5 to 4 seconds and preferably 1 second. This can be easily obtained in different manners known and appreciated by those skilled in the art. For example, a valve with a frusto conical bushel or a set of two valves mounted in parallel, one of which has a small diameter, may be employed. A more advanced method would be to use an automatically programmed opening.

The process according to my invention is particularly advantageous when the flow of the metal along the container, die and mandrel is lubricated with a glass-like material. Because of the large bore diameter in comparison to the mandrel diameter, the mandrel does not come into contact with the billet when running into it and, therefore, the lubricating filmprepared for the bore surface is kept unbroken and uniform.

When the force of the press is first applied, the metal is initially pushed into contact with the whole container wall. Thereafter, the metal comes into contact with the mandrel at its leading end, so that the leading end traps and retains the lubricant prepared for the bore surface. This deformation requires a force 2 to 5 times smaller than needed for the extrusion itself. Therefore, it is practically completed before any incipient extrusion, so that the extrusion starts symmetrically and the mandrel retains a correctly centered position.

Since the clearance between the billet bore and the mandrel may lie within a rather wide range, it is possible to have only the one billet bore for a set of mandrels, the diameters of which are within a certain interval. This results in savings in piercing tools.

Since the bore of the billet has a larger diameter than employed heretofore, the bore can be obtained by hot piercing a solid billet with a satisfactory concentricity, even if the pierced billet is longer.

Due to the progressive application of the extrusion force, the extrusion itself, which follows the upsetting, can slowly start slightly before the full force has been applied, so that the veins of flowing metal are formed gently and the regular flow of the metal gives a well centered tube from the very beginning.

Moreover, this progressive application avoids the overpressure usually experienced at the beginning of the extrusion and the related tool wear. It is, therefore, possible to use under the running extrusion condition substantially the whole force of the press, since no provision has to be made for the starting overpressure. This permits an increase in the extrusion ratio which *ca'ribe defined by the container cross sectional area minus the mandrel cross sectional area over the die cross sectional area minus the mandrel cross sectional area.

EXAMPLE Carbon steel tubes 150 mm (5.91 inches) in outside diameter, 17.5 mm (0.69 inch) in wall thickness have been extruded from a horizontal hydraulic 3, 100 metric ton press equipped with a container 345 mm (13.58 inches) in diameter and a mandrel l mm (4.53 inches) in diameter.

The press was actuated through a valve with a frusto conical bushel which permitted the control of the rate of pressure increase. The starting material was carbon steel billets previously hot pierced to an inside diameter of 160 mm (6.30 inches), an outside diameter of 340 mm (13.39 inches) and a length of 1,100 mm (43.31

inches) so that the diametral clearance between the bore of the billet and the mandrel was 19.7 percent of. the difference between the container and mandrel diameters. The bushel valve was operated so that the full pressure was established after one second.

The tubes produced were 10,800 meters (35.42 feet) in length. They all showed a perfect concentricity and excellent surface condition on both the inside and outside of the tubing. This proved satisfactory that the lubrication had been uniformly distributed and had been satisfactory through the entire extrusion.

According to the current practices, the billet would have been pierced to a diameter of about mm (4.72 inches) and the pressure would have been established without any delay. Under these conditions, some of the tubes would have shown surface defects and there would have been a risk of having stickers. Moreover, hot piercing billets with a bore diameter of 120 mm (4.720 inches) and with the same concentricity would have produced a final length of the billet of 825 mm (32.48 inches) so that the length of the tube would not have exceed 9,800 meters (32.14 feet).

1. In a process for hot extruding metal tubing from billets in a hydraulic press including a container, a die, and a mandrel, the improvement comprising piercing the billet to a bore diameter substantially greater than that of the extrusion mandrel prior to insertion of the billet into the container and progressively applying the force of the press to deform and extrude the billet into metal tubing, said progressive application of force corresponding to a time interval from 0.5 to 4 seconds between the initial pressure increase and the completion in a cylinder of the hydraulic press of the maximum available pressure.

2. The improvement of claim 1 wherein the bore diameter exceeds the mandrel diameter by an amount of from 5 to 30 percent of the difference between the container diameter and the extrusion mandrel diameter.

I 3. The improvement of claim 1 wherein the bore diameter exceeds the mandrel diameter by an amount of about 20 percent of the difference between the container diameter and the extrusionmandrel diameter.

4. The improvement of claim 1 including the step of lubricating the metal flow along at least one of the container wall, the die and the mandrel with a glass-like material simultaneous with the extruding of the billet.

5. The improvement of claim 1 wherein said progressive application of force corresponds to a time interval of about 1 second. 

1. In a process for hot extruding metal tubing from billets in a hydraulic press including a container, a die, and a mandrel, the improvement comprising piercing the billet to a bore diameter substantially greater than that of the Extrusion mandrel prior to insertion of the billet into the container and progressively applying the force of the press to deform and extrude the billet into metal tubing, said progressive application of force corresponding to a time interval from 0.5 to 4 seconds between the initial pressure increase and the completion in a cylinder of the hydraulic press of the maximum available pressure.
 2. The improvement of claim 1 wherein the bore diameter exceeds the mandrel diameter by an amount of from 5 to 30 percent of the difference between the container diameter and the extrusion mandrel diameter.
 3. The improvement of claim 1 wherein the bore diameter exceeds the mandrel diameter by an amount of about 20 percent of the difference between the container diameter and the extrusion mandrel diameter.
 4. The improvement of claim 1 including the step of lubricating the metal flow along at least one of the container wall, the die and the mandrel with a glass-like material simultaneous with the extruding of the billet.
 5. The improvement of claim 1 wherein said progressive application of force corresponds to a time interval of about 1 second. 